Maternal antibodies enhance or prevent cytomegalovirus infection in the placenta by neonatal Fc receptor-mediated transcytosis

Zika Virus: Medical Countermeasure Development Challenges

INTRODUCTION

Reports of high rates of primary microcephaly and Guillain-Barré syndrome associated with Zika virus infection in French Polynesia and Brazil have raised concerns that the virus circulating in these regions is a rapidly developing neuropathic, teratogenic, emerging infectious public health threat. There are no licensed medical countermeasures (vaccines, therapies or preventive drugs) available for Zika virus infection and disease. The Pan American Health Organization (PAHO) predicts that Zika virus will continue to spread and eventually reach all countries and territories in the Americas with endemic Aedes mosquitoes. This paper reviews the status of the Zika virus outbreak, including medical countermeasure options, with a focus on how the epidemiology, insect vectors, neuropathology, virology and immunology inform options and strategies available for medical countermeasure development and deployment.

METHODS

Multiple information sources were employed to support the review. These included publically available literature, patents, official communications, English and Lusophone lay press. Online surveys were distributed to physicians in the US, Mexico and Argentina and responses analyzed. Computational epitope analysis as well as infectious disease outbreak modeling and forecasting were implemented. Field observations in Brazil were compiled and interviews conducted with public health officials.

Evidence that FcRn mediates the transplacental passage of maternal IgE in the form of IgG anti-IgE/IgE immune complexes

BACKGROUND

The mechanism(s) responsible for acquisition of maternal antibody isotypes other than IgG are not fully understood. This uncertainty is a major reason underlying the continued controversy regarding whether cord blood (CB) IgE originates in the mother or fetus.

OBJECTIVE

To investigate the capacity of maternal IgE to be transported across the placenta in the form of IgG anti-IgE/IgE immune complexes (ICs) and to determine the role of the neonatal Fc receptor (FcRn) in mediating this process.

METHODS

Maternal and CB serum concentrations of IgE, IgG anti-IgE, and IgG anti-IgE/IgE ICs were determined in a cohort of allergic and non-allergic mother/infant dyads. Madin-Darby canine kidney (MDCK) cells stably transfected with human FcRn were used to study the binding and transcytosis of IgE in the form of IgG anti-IgE/IgE ICs.

RESULTS

Maternal and CB serum concentrations of IgG anti-IgE/IgE ICs were highly correlated, regardless of maternal allergic status. IgG anti-IgE/IgE ICs generated in vitro bound strongly to FcRn-expressing MDCK cells and were transcytosed in an FcRn-dependent manner. Conversely, monomeric IgE did not bind to FcRn and was not transcytosed. IgE was detected in solutions of transcytosed IgG anti-IgE/IgE ICs, even though essentially all the IgE remained in complex form. Similarly, the majority of IgE in CB sera was found to be complexed to IgG.

CONCLUSIONS AND CLINICAL RELEVANCE

These data indicate that human FcRn facilitates the transepithelial transport of IgE in the form of IgG anti-IgE/IgE ICs. They also strongly suggest that the majority of IgE in CB sera is the result of FcRn-mediated transcytosis of maternal-derived IgG anti-IgE/IgE ICs. These findings challenge the widespread perception that maternal IgE does not cross the placenta. Measuring maternal or CB levels of IgG anti-IgE/IgE ICs may be a more accurate predictor of allergic risk.

Maternal CD4+ T cells protect against severe congenital cytomegalovirus disease in a novel nonhuman primate model of placental cytomegalovirus transmission

Elucidation of maternal immune correlates of protection against congenital cytomegalovirus (CMV) is necessary to inform future vaccine design. Here, we present a novel rhesus macaque model of placental rhesus CMV (rhCMV) transmission and use it to dissect determinants of protection against congenital transmission following primary maternal rhCMV infection. In this model, asymptomatic intrauterine infection was observed following i.v. rhCMV inoculation during the early second trimester in two of three rhCMV-seronegative pregnant females. In contrast, fetal loss or infant CMV-associated sequelae occurred in four rhCMV-seronegative pregnant macaques that were CD4(+) T-cell depleted at the time of inoculation. Animals that received the CD4(+) T-cell-depleting antibody also exhibited higher plasma and amniotic fluid viral loads, dampened virus-specific CD8(+) T-cell responses, and delayed production of autologous neutralizing antibodies compared with immunocompetent monkeys. Thus, maternal CD4(+) T-cell immunity during primary rhCMV infection is important for controlling maternal viremia and inducing protective immune responses that prevent severe CMV-associated fetal disease.

Role of human cytomegalovirus in the proliferation and invasion of extravillous cytotrophoblasts isolated from early placentae

AIM

We investigated the role of human cytomegalovirus (HCMV) and its mechanism in extravillous cytotrophoblast (EVT) proliferation and invasion in vitro.

METHODS

Differential enzymatic digestion combined with gradient centrifugation, was used to isolate primary EVT from human chorionic villi collected from early placentae of healthy pregnant women. HCMV infection was determined by immunofluorescence staining of HCMVpp65 antigen expression. An MTT assay was used to examine the role of HCMV in the proliferation of EVT. Quantitative real-time polymerase chain reaction (qRT-PCR), immunocytochemical staining and Western blots were carried out in a control group (EVT) and a virus group (EVT+HCMV) to examine the expression of major genes and protein in TGF-β/Smad signaling pathways in EVT 48 h after inoculation with HCMV. An in vitro cell invasion assay was performed to analyze the influence of HCMV on EVT invasion.

RESULTS

HCMV significantly inhibited the proliferation of EVT 48 h after viral infection (P < 0.05). The expression of TGF-β1, Smad1, Smad2, Smad3, Smad4, and Smad5 genes was significantly increased (P < 0.05), but that of TGF-β2, TGF-β3, TGFβRI, TGFβRII, Smad7, MMP2, and MMP9 was significantly decreased in the virus group 48 h after HCMV infection (P < 0.05). Smad7, MMP-2 and MMP-9 protein levels were significantly decreased and the TGF-β1 protein level was significantly increased in infected EVT (all P < 0.05).

CONCLUSIONS

HCMV may act on multiple steps of the TGF-β/Smad signaling pathway to impede EVT proliferation and invasion.

Vaccine-Derived Neutralizing Antibodies to the Human Cytomegalovirus gH/gL Pentamer Potently Block Primary Cytotrophoblast Infection

Human cytomegalovirus (HCMV) elicits neutralizing antibodies (NAb) of various potencies and cell type specificities to prevent HCMV entry into fibroblasts (FB) and epithelial/endothelial cells (EpC/EnC). NAb targeting the major essential envelope glycoprotein complexes gB and gH/gL inhibit both FB and EpC/EnC entry. In contrast to FB infection, HCMV entry into EpC/EnC is additionally blocked by extremely potent NAb to conformational epitopes of the gH/gL/UL128/130/131A pentamer complex (PC). We recently developed a vaccine concept based on coexpression of all five PC subunits by a single modified vaccinia virus Ankara (MVA) vector, termed MVA-PC. Vaccination of mice and rhesus macaques with MVA-PC resulted in a high titer and sustained NAb that blocked EpC/EnC infection and lower-titer NAb that inhibited FB entry. However, antibody function responsible for the neutralizing activity induced by the MVA-PC vaccine is uncharacterized. Here, we demonstrate that MVA-PC elicits NAb with cell type-specific neutralization potency and antigen recognition pattern similar to human NAb targeting conformational and linear epitopes of the UL128/130/131A subunits or gH. In addition, we show that the vaccine-derived PC-specific NAb are significantly more potent than the anti-gH NAb to prevent HCMV spread in EpC and infection of human placental cytotrophoblasts, cell types thought to be of critical importance for HCMV transmission to the fetus. These findings further validate MVA-PC as a clinical vaccine candidate to elicit NAb that resembles those induced during HCMV infection and provide valuable insights into the potency of PC-specific NAb to interfere with HCMV cell-associated spread and infection of key placental cells.

IMPORTANCE

As a consequence of the leading role of human cytomegalovirus (HCMV) in causing permanent birth defects, developing a vaccine against HCMV has been assigned a major public health priority. We have recently introduced a vaccine strategy based on a widely used, safe, and well-characterized poxvirus vector platform to elicit potent and durable neutralizing antibody (NAb) responses targeting the HCMV envelope pentamer complex (PC), which has been suggested as a critical component for a vaccine to prevent congenital HCMV infection. With this work, we confirm that the NAb elicited by the vaccine vector have properties that are similar to those of human NAb isolated from individuals chronically infected with HCMV. In addition, we show that PC-specific NAb have potent ability to prevent infection of key placental cells that HCMV utilizes to cross the fetal-maternal interface, suggesting that NAb targeting the PC may be essential to prevent HCMV vertical transmission.

FcRn: The Architect Behind the Immune and Nonimmune Functions of IgG and Albumin

The neonatal FcR (FcRn) belongs to the extensive and functionally divergent family of MHC molecules. Contrary to classical MHC family members, FcRn possesses little diversity and is unable to present Ags. Instead, through its capacity to bind IgG and albumin with high affinity at low pH, it regulates the serum half-lives of both of these proteins. In addition, FcRn plays an important role in immunity at mucosal and systemic sites through its ability to affect the lifespan of IgG, as well as its participation in innate and adaptive immune responses. Although the details of its biology are still emerging, the ability of FcRn to rescue albumin and IgG from early degradation represents an attractive approach to alter the plasma half-life of pharmaceuticals. We review some of the most novel aspects of FcRn biology, immune as well as nonimmune, and provide some examples of FcRn-based therapies.

Passive Immunization against Congenital Cytomegalovirus Infection: Current State of Knowledge

Primary infection with the human cytomegalovirus (CMV) occurs in 1-4% of pregnancies. The rates of maternal-fetal CMV transmissions are around 25, 36, 41, and 66%, for infections occurring in the peri-conceptional weeks, first, second, and third trimester of pregnancy, respectively. On the other hand, the severity of fetal organ damage and dysfunction diminishes with increasing gestational age. Congenitally CMV-infected newborns may have neurosensory impairments like mental retardation, cerebral palsy, epilepsy, progressive hearing loss or visual defects, or even may have a fatal outcome. In in-vitro experiments, CMV specific neutralizing IgG antibodies - which are abundant in CMV specific hyperimmune globulin (HIG) products - inhibited the entry of the virus into target cells and hampered viral cell-to-cell spread. This article provides a brief overview on the epidemiology and diagnostic tools in congenital CMV infection. It also concisely summarizes the currently available study results on the safety and effectiveness of HIG treatment. Accordingly, in clinical studies HIG administration to expectant mothers following primary CMV infection (prophylactic use) was shown to lower the risk of maternal-fetal transmission of CMV compared to untreated controls. HIG was also able to ameliorate the disease sequelae in evidently infected fetuses (therapeutic use), as demonstrated by the regression or even resolution of sonographic pathologies including placental inflammation.

Placental Hofbauer cells assemble and sequester HIV-1 in tetraspanin-positive compartments that are accessible to broadly neutralizing antibodies

Introduction

Within monocyte-derived macrophages, HIV-1 accumulates in intracellular virus-containing compartments (VCCs) that are inaccessible to the external environment, which implicate these cells as latently infected HIV-1 reservoirs. During mother-to-child transmission of HIV-1, human placental macrophages (Hofbauer cells (HCs)) are viral targets, and have been shown to be infected in vivo and sustain low levels of viral replication in vitro; however, the risk of in utero transmission is less than 7%. The role of these primary macrophages as viral reservoirs is largely undefined. The objective of this study is to define potential sites of viral assembly, accumulation and neutralization in HCs given the pivotal role of the placenta in preventing HIV-1 infection in the mother-infant dyad.

Methods

Term placentae from 20 HIV-1 seronegative women were obtained following caesarian section. VCCs were evaluated by 3D confocal and electron microscopy. Colocalization R values (Pearson's correlation) were quantified with colocalization module of Volocity 5.2.1. Replication kinetics and neutralization studies were evaluated using p24 ELISA.

Results

We demonstrate that primary HCs assemble and sequester HIV-1_BaL in intracellular VCCs, which are enriched in endosomal/lysosomal markers, including CD9, CD81, CD63 and LAMP-1. Following infection, we observed HIV-1 accumulation in potentially acidic compartments, which stained intensely with Lysotracker-Red. Remarkably, these compartments are readily accessible via the cell surface and can be targeted by exogenously applied small molecules and HIV-1-specific broadly neutralizing antibodies. In addition, broadly neutralizing antibodies (4E10 and VRC01) limited viral replication by HIV-1-infected HCs, which may be mediated by FcγRI.

Conclusions

These findings suggest that placental HCs possess intrinsic adaptations facilitating unique sequestration of HIV-1, and may serve as a protective viral reservoir to permit viral neutralization and/or antiretroviral drug entry in utero.

[The role of virological tests in the diagnosis of cytomegalovirus infection in pregnant women]

INTRODUCTION

The most harmful and most frequent foetal agent is cytomegalovirus. The progress in diagnostic tools and therapeutic opportunities opened new perspectives in the diagnosis and management of foetal cytomegalovirus infection.

AIM

Evaluation of cytomegalovirus virological test results performed during pregnancy between 2007 and 2012.

METHOD

Clinical and virology data were retrospectively analysed.

RESULTS

64.5% of the 956 tested women were serologically protected and 33.3% were susceptible to cytomegalovirus. Recent infection was confirmed in 10 pregnant women, while the infection could not be confirmed or excluded in 3 pregnant women. Six pregnant women were asymptomatic, 5 had typical disease, and 2 had abnormal fetal ultrasound. One fetus aborted, congenital infection was confirmed in 2, and was excluded in one of the four newborns tested.

CONCLUSIONS

The immunity of women to cytomegalovirus reflects high socioeconomic circumstances. Confimatory tests must be done both in women who have cytomegalovirus disease and those who have IgM positive result detected by enzyme (linked) immunoassay. Screening must be done prior to pregnancy. Strict collaboration between professionals of different medical specialties is necessary.

Regulation of immune responses by the neonatal fc receptor and its therapeutic implications

As a single receptor, the neonatal Fc receptor (FcRn) is critically involved in regulating albumin and IgG serum concentrations by protecting these two ligands from degradation. In addition to these essential homeostatic functions, FcRn possesses important functions in regulating immune responses that are equally as critical and are increasingly coming to attention. During the first stages of life, FcRn mediates the passive transfer of IgG across the maternal placenta or neonatal intestinal walls of mammals, thereby conferring passive immunity to the offspring before and after birth. In fact, FcRn is one of the very few molecules that are known to move from luminal to serosal membranes of polarized cells that form epithelial barriers of the lung and intestines. Together with FcRn's recently explored critical role in eliciting MHC II presentation and MHC class I cross-presentation of IgG-complexed antigen, this renders FcRn capable of exerting broad and potent functions in regulating immune responses and immunosurveillance at mucosal sites. Further, it is now clear that FcRn dependent mucosal absorption of therapeutic molecules is a clinically feasible and potent novel route of non-invasive drug delivery, and the interaction between FcRn and IgG has also been utilized for the acquisition of humoral immunity at mucosal sites. In this review, we begin by briefly summarizing the basic knowledge on FcRn expression and IgG binding, then describe more recent discoveries pertaining to the mechanisms by which FcRn orchestrates IgG related mucosal immune responses and immunosurveillance at host-environment interfaces within the adult organism. Finally, we outline how the knowledge of actions of FcRn at mucosal boundaries can be capitalized for the development and engineering of powerful mucosal vaccination strategies and novel routes for the non-invasive delivery of Fc-based therapeutics.

Cytomegalovirus infection and pathogenesis in the human placenta

Human cytomegalovirus (HCMV) is the most common cause of congenital viral infection. Affected children can have permanent neurological complications, including hearing loss, visual impairment and mental retardation1–3. In Australia, 57% of women are seronegative and at risk for primary infection and transmission of virus to the fetus during pregnancy4. Despite its public health significance, the specific molecular and cellular basis of HCMV replication in the human placenta and pathogenesis associated with poor clinical outcome are unknown. Direct fetal infection is involved in severe cases of neuropathology and infection of the placenta can impair its development and functions resulting in a hypoxic environment5–8 and stillbirth6,9,10. Gestational age at the time of infection is an important determinant of outcome. The rates of virus transmission increase from 30% in first trimester to over 70% in third trimester suggesting different mechanisms for overcoming the placental barrier2. Remarkable insights into viral pathogenesis factors that function in the tissue environment have been gained by studying congenitally infected placentas and explants infected by clinical strains ex vivo. Together these studies revealed that direct infection of specialised placental cells and paracrine factors contribute to impaired development and functional defects.

Vaccination for cytomegalovirus: when, where and how

Although following primary human cytomegalovirus (CMV) infection in many individuals no overt symptoms are observed, CMV came to medical attention due to its significant morbidity and mortality associated with congenital infection and immunosuppressed individuals. Congenital infection occurs following transplacental transmission during pregnancy as a result of primary infection, reactivation or re-infection with a different isolate. Estimates suggest at least a million cases of congenital CMV occur annually worldwide. Congenital infection is a leading cause of neurological complications such as mental retardation, cerebral palsy, developmental delay and seizure disorders and also causes permanent disabilities, such as hearing loss and vision impairment. In addition, other common manifestation of CMV infection are stillbirth, preterm delivery and intrauterine growth restriction (IUGR) and cardiovascular disease, which are risk factors for perinatal and lifetime morbidity. Recent reports have estimated that the economic costs to public health and families due to congenital CMV infection are immense, with direct annual costs of billions of dollars. An effective CMV vaccine that could prevent transplacental transmission, reduce CMV disease and CMV-associated stillbirths has been recognised as an urgent medical need. Over the past 40 years several CMV vaccine candidates have been evaluated in a series of clinical trials and found to be effective in preclinical and clinical studies. However, in spite of extensive efforts over many decades, successful licensure of an effective CMV vaccine formulation to prevent congenital CMV infection remains elusive.

A high-affinity native human antibody neutralizes human cytomegalovirus infection of diverse cell types

Human cytomegalovirus (HCMV) is the most common infection causing poor outcomes among transplant recipients. Maternal infection and transplacental transmission are major causes of permanent birth defects. Although no active vaccines to prevent HCMV infection have been approved, passive immunization with HCMV-specific immunoglobulin has shown promise in the treatment of both transplant and congenital indications. Antibodies targeting the viral glycoprotein B (gB) surface protein are known to neutralize HCMV infectivity, with high-affinity binding being a desirable trait, both to compete with low-affinity antibodies that promote the transmission of virus across the placenta and to displace nonneutralizing antibodies binding nearby epitopes. Using a miniaturized screening technology to characterize secreted IgG from single human B lymphocytes, 30 antibodies directed against gB were previously cloned. The most potent clone, TRL345, is described here. Its measured affinity was 1 pM for the highly conserved site I of the AD-2 epitope of gB. Strain-independent neutralization was confirmed for 15 primary HCMV clinical isolates. TRL345 prevented HCMV infection of placental fibroblasts, smooth muscle cells, endothelial cells, and epithelial cells, and it inhibited postinfection HCMV spread in epithelial cells. The potential utility for preventing congenital transmission is supported by the blockage of HCMV infection of placental cell types central to virus transmission to the fetus, including differentiating cytotrophoblasts, trophoblast progenitor cells, and placental fibroblasts. Further, TRL345 was effective at controlling an ex vivo infection of human placental anchoring villi. TRL345 has been utilized on a commercial scale and is a candidate for clinical evaluation.

Human cytomegalovirus vaccine based on the envelope gH/gL pentamer complex

Human Cytomegalovirus (HCMV) utilizes two different pathways for host cell entry. HCMV entry into fibroblasts requires glycoproteins gB and gH/gL, whereas HCMV entry into epithelial and endothelial cells (EC) requires an additional complex composed of gH, gL, UL128, UL130, and UL131A, referred to as the gH/gL-pentamer complex (gH/gL-PC). While there are no established correlates of protection against HCMV, antibodies are thought to be important in controlling infection. Neutralizing antibodies (NAb) that prevent gH/gL-PC mediated entry into EC are candidates to be assessed for in vivo protective function. However, these potent NAb are predominantly directed against conformational epitopes derived from the assembled gH/gL-PC. To address these concerns, we constructed Modified Vaccinia Ankara (MVA) viruses co-expressing all five gH/gL-PC subunits (MVA-gH/gL-PC), subsets of gH/gL-PC subunits (gH/gL or UL128/UL130/UL131A), or the gB subunit from HCMV strain TB40/E. We provide evidence for cell surface expression and assembly of complexes expressing full-length gH or gB, or their secretion when the corresponding transmembrane domains are deleted. Mice or rhesus macaques (RM) were vaccinated three times with MVA recombinants and serum NAb titers that prevented 50% infection of human EC or fibroblasts by HCMV TB40/E were determined. NAb responses induced by MVA-gH/gL-PC blocked HCMV infection of EC with potencies that were two orders of magnitude greater than those induced by MVA expressing gH/gL, UL128-UL131A, or gB. In addition, MVA-gH/gL-PC induced NAb responses that were durable and efficacious to prevent HCMV infection of Hofbauer macrophages, a fetal-derived cell localized within the placenta. NAb were also detectable in saliva of vaccinated RM and reached serum peak levels comparable to NAb titers found in HCMV hyperimmune globulins. This vaccine based on a translational poxvirus platform co-delivers all five HCMV gH/gL-PC subunits to achieve robust humoral responses that neutralize HCMV infection of EC, placental macrophages and fibroblasts, properties of potential value in a prophylactic vaccine.

Human cytomegalovirus (HCMV) fetal infection during pregnancy and infection of immunocompromised patients are both clinical problems considered extremely important by the Institute of Medicine. Limited efficacy against primary HCMV infection was found using a subunit vaccine based on glycoprotein B, an important neutralizing antibody determinant blocking HCMV entry into fibroblasts. The HCMV field has been transformed by the discovery that a five-member (pentamer) protein complex is a required factor for epithelial and endothelial cell entry and indispensable for transmission as shown in non-human primates. Targeting HCMV with antibodies specific to the pentamer may interrupt horizontal and vertical transmission. We describe an innovative vaccine strategy to induce serum neutralizing antibodies of impressive magnitude against HCMV in two animal models. Using an attenuated poxvirus vector system, we demonstrate that co-expression of all five pentamer components is significantly more potent to induce serum neutralizing antibodies than subunit subsets of the complex or glycoprotein B, reaching peak levels comparable to HCMV hyperimmune globulin. A vaccine that elicits systemic and mucosal antibody responses that prevents infection of multiple cell types crucial to natural history of HCMV infection could play a role in preventing congenital HCMV infection and control of infection in immunocompromised patients.

Ex vivo model of congenital cytomegalovirus infection and new combination therapies

INTRODUCTION

Congenital human cytomegalovirus (HCMV) infection is a major public health problem due to severe sequelae in the fetus and newborns. Currently, due to their toxicity anti-CMV treatments cannot be administered to pregnant women. We thus developed an ex vivo model of 1(st) trimester placental CMV infection to observe the route of infection across the placenta and to test the efficacy of various new drugs targeting different stages of viral cycle.

METHODS

After validation of the viability of floating villi explants by ELISA β-HCG, the kinetics of placental infection were determined by immunochemistry and qPCR in this ex vivo model. Antiviral susceptibility was determined in vitro using focus reduction assay and by qPCR in the ex vivo model.

RESULTS

The ex vivo model showed viral infection in trophoblasts and mesenchymal space of floating villi. In vitro, antiviral combinations of maribavir with baïcalein or artesunate inhibited viral infection by more than 90%. On the other hand, in ex vivo model, infection was reduced by 40% in presence of maribavir and artesunate. The synergistic effect observed in vitro was not observed ex vivo.

DISCUSSION

This model allowed us to understand the CMV spread in 1(st) trimester floating villi better and to analyze the anti-CMV efficacy and toxicity of new drugs that could be administered to pregnant women, either alone or in combination.

CONCLUSIONS

Such an ex vivo model could be applied to other viruses such as rubella or parvovirus B19 and in new drug development.

Models of vertical cytomegalovirus (CMV) transmission and pathogenesis

Despite the considerable clinical impact of congenital human cytomegalovirus (HCMV) infection, the mechanisms of maternal-fetal transmission and the resultant placental and fetal damage are largely unknown. Here, we discuss animal models for the evaluation of CMV vaccines and virus-induced pathology and particularly explore surrogate human models for HCMV transmission and pathogenesis in the maternal-fetal interface. Studies in floating and anchoring placental villi and more recently, ex vivo modeling of HCMV infection in integral human decidual tissues, provide unique insights into patterns of viral tropism, spread, and injury, defining the outcome of congenital infection, and the effect of potential antiviral interventions.

Live simian immunodeficiency virus vaccine correlate of protection: local antibody production and concentration on the path of virus entry

We sought design principles for a vaccine to prevent HIV transmission to women by identifying correlates of protection conferred by a highly effective live attenuated SIV vaccine in the rhesus macaque animal model. We show that SIVmac239Δnef vaccination recruits plasma cells and induces ectopic lymphoid follicle formation beneath the mucosal epithelium in the rhesus macaque female reproductive tract. The plasma cells and ectopic follicles produce IgG Abs reactive with viral envelope glycoprotein gp41 trimers, and these Abs are concentrated on the path of virus entry by the neonatal FcR in cervical reserve epithelium and in vaginal epithelium. This local Ab production and delivery system correlated spatially and temporally with the maturation of local protection against high-dose pathogenic SIV vaginal challenge. Thus, designing vaccines to elicit production and concentration of Abs at mucosal frontlines could aid in the development of an effective vaccine to protect women against HIV-1.

Immunobiology of congenital cytomegalovirus infection of the central nervous system—the murine cytomegalovirus model

Congenital human cytomegalovirus infection is a leading infectious cause of long-term neurodevelopmental sequelae, including mental retardation and hearing defects. Strict species specificity of cytomegaloviruses has restricted the scope of studies of cytomegalovirus infection in animal models. To investigate the pathogenesis of congenital human cytomegalovirus infection, we developed a mouse cytomegalovirus model that recapitulates the major characteristics of central nervous system infection in human infants, including the route of neuroinvasion and neuropathological findings. Following intraperitoneal inoculation of newborn animals with mouse cytomegalovirus, the virus disseminates to the central nervous system during high-level viremia and replicates in the brain parenchyma, resulting in a focal but widespread, non-necrotizing encephalitis. Central nervous system infection is coupled with the recruitment of resident and peripheral immune cells as well as the expression of a large number of pro-inflammatory cytokines. Although infiltration of cellular constituents of the innate immune response characterizes the early immune response in the central nervous system, resolution of productive infection requires virus-specific CD8(+) T cells. Perinatal mouse cytomegalovirus infection results in profoundly altered postnatal development of the mouse central nervous system and long-term motor and sensory disabilities. Based on an enhanced understanding of the pathogenesis of this infection, prospects for novel intervention strategies aimed to improve the outcome of congenital human cytomegalovirus infection are proposed.

Cytomegalovirus infection and antibody protection of the developing placenta

Human cytomegalovirus (HCMV) infection is transmitted from the infected mother to the placenta and fetus. Virus replicates in the decidua, invasive cytotrophoblasts that breach the uterine vasculature and villous cytotrophoblasts underlying syncytiotrophoblasts, then reaches blood vessels in the villus core. Virus replication, fibrosis, and edema result in a hypoxic intrauterine environment and release of cytokines that stimulates compensatory development of the placenta. We employed villous explant cultures to study viral effects on differentiation and test novel approaches to rescue the placenta from infection.

A neutralizing anti-gH/gL monoclonal antibody is protective in the guinea pig model of congenital CMV infection

Human cytomegalovirus (HCMV) is the most common cause of congenital virus infection. Congenital HCMV infection occurs in 0.2–1% of all births, and causes birth defects and developmental abnormalities, including sensorineural hearing loss and developmental delay. Several key studies have established the guinea pig as a tractable model for the study of congenital HCMV infection and have shown that polyclonal antibodies can be protective [1]–[3]. In this study, we demonstrate that an anti-guinea pig CMV (GPCMV) glycoprotein H/glycoprotein L neutralizing monoclonal antibody protects against fetal infection and loss in the guinea pig. Furthermore, we have delineated the kinetics of GPCMV congenital infection, from maternal infection (salivary glands, seroconversion, placenta) to fetal infection (fetus and amniotic fluid). Our studies support the hypothesis that a neutralizing monoclonal antibody targeting an envelope GPCMV glycoprotein can protect the fetus from infection and may shed light on the therapeutic intervention of HCMV congenital infection in humans.

Human cytomegalovirus (HCMV) is the most common cause of congenital virus infection and causes developmental abnormalities, including hearing loss and developmental delay. Although there is no therapy for congenital HCMV disease, there is evidence from both human and animal studies that antibodies can have efficacy in this setting. Such studies have focused exclusively on polyclonal antibodies, in which the targets of protective antibodies are unknown. Guinea pigs have been used as a model of human maternal fetal transmission of infection because of similarities in placental anatomy between human and guinea pig. Furthermore, guinea pig CMV (GPCMV) has been demonstrated to cross the placenta and cause fetal infection and loss, similar to the effects of infection with HCMV. However, the kinetics of maternal and fetal infection in this model has not been carefully investigated. In this work, we have delineated the kinetics of maternal to fetal infection and found that congenital infection is rapid following maternal infection. Importantly, we demonstrate that a monoclonal antibody against a protein critical for viral entry protects pregnant guinea pigs against fetal infection. Thus, our studies may be informative for development of a therapeutic intervention to treat congenital HCMV infection in humans.

HCMV infection of human trophoblast progenitor cells of the placenta is neutralized by a human monoclonal antibody to glycoprotein B and not by antibodies to the pentamer complex

Human cytomegalovirus (HCMV) is the major viral cause of congenital infection and birth defects. Primary maternal infection often results in virus transmission, and symptomatic babies can have permanent neurological deficiencies and deafness. Congenital infection can also lead to intrauterine growth restriction, a defect in placental transport. HCMV replicates in primary cytotrophoblasts (CTBs), the specialized cells of the placenta, and inhibits differentiation/invasion. Human trophoblast progenitor cells (TBPCs) give rise to the mature cell types of the chorionic villi, CTBs and multi-nucleated syncytiotrophoblasts (STBs). Here we report that TBPCs are fully permissive for pathogenic and attenuated HCMV strains. Studies with a mutant virus lacking a functional pentamer complex (gH/gL/pUL128-131A) showed that virion entry into TBPCs is independent of the pentamer. In addition, infection is blocked by a potent human neutralizing monoclonal antibody (mAb), TRL345, reactive with glycoprotein B (gB), but not mAbs to the pentamer proteins pUL130/pUL131A. Functional studies revealed that neutralization of infection preserved the capacity of TBPCs to differentiate and assemble into trophospheres composed of CTBs and STBs in vitro. Our results indicate that mAbs to gB protect trophoblast progenitors of the placenta and could be included in antibody treatments developed to suppress congenital infection and prevent disease.

Multiplexed screening of natural humoral immunity identifies antibodies at fine specificity for complex and dynamic viral targets

Viral entry targets with therapeutic neutralizing potential are subject to multiple escape mechanisms, including antigenic drift, immune dominance of functionally irrelevant epitopes, and subtle variations in host cell mechanisms. A surprising finding of recent years is that potent neutralizing antibodies to viral epitopes independent of strain exist, but are poorly represented across the diverse human population. Identifying these antibodies and understanding the biology mediating the specific immune response is thus difficult. An effective strategy for meeting this challenge is to incorporate multiplexed antigen screening into a high throughput survey of the memory B cell repertoire from immune individuals. We used this approach to discover suites of cross-clade antibodies directed to conformational epitopes in the stalk region of the influenza A hemagglutinin (HA) protein and to select high-affinity anti-peptide antibodies to the glycoprotein B (gB) of human cytomegalovirus. In each case, our screens revealed a restricted VH and VL germline usage, including published and previously unidentified gene families. The in vivo evolution of paratope specificity with optimal neutralizing activity was understandable after correlating biological activities with kinetic binding and epitope recognition. Iterative feedback between antigen probe design based on structure and function information with high throughput multiplexed screening demonstrated a generally applicable strategy for efficient identification of safe, native, finely tuned antibodies with the potential for high genetic barriers to viral escape.

Intrauterine growth restriction caused by underlying congenital cytomegalovirus infection

BACKGROUND

Human cytomegalovirus (HCMV) is the major viral etiology of congenital infection and birth defects. Fetal transmission is high (30%-40%) in primary maternal infection, and symptomatic babies have permanent neurological, hearing, and vision defects. Recurrent infection is infrequently transmitted (2%) and largely asymptomatic. Congenital infection is also associated with intrauterine growth restriction (IUGR).

METHODS

To investigate possible underlying HCMV infection in cases of idiopathic IUGR, we studied maternal and cord sera and placentas from 19 pregnancies. Anti-HCMV antibodies, hypoxia-related factors, and cmvIL-10 were measured in sera. Placental biopsy specimens were examined for viral DNA, expression of infected cell proteins, and pathology.

RESULTS

Among 7 IUGR cases, we identified 2 primary and 3 recurrent HCMV infections. Virus replicated in glandular epithelium and lymphatic endothelium in the decidua, cytotrophoblasts, and smooth muscle cells in blood vessels of floating villi and the chorion. Large fibrinoids with avascular villi, edema, and inflammation were significantly increased. Detection of viral proteins in the amniotic epithelium indicated transmission in 2 cases of IUGR with primary infection and 3 asymptomatic recurrent infections.

CONCLUSIONS

Congenital HCMV infection impairs placental development and functions and should be considered as an underlying cause of IUGR, regardless of virus transmission to the fetus.

Recent approaches and strategies in the generation of antihuman cytomegalovirus vaccines

The development of prophylactic and to lesser extent therapeutic vaccines for the prevention of disease associated with human cytomegalovirus (HCMV) infections has received considerable attention from biomedical researchers and pharmaceutical companies over the previous 15 years, even though attempts to produce such vaccines have been described in the literature for over 40 years. Studies of the natural history of congenital HCMV infection and infection in allograft recipients have suggested that prophylaxis of disease associated with HCMV infection could be possible, particularly in hosts at risk for more severe disease secondary to the lack of preexisting immunity. Provided a substantial understanding of immune response to HCMV together with several animal models that faithfully recapitulate aspects of human infection and immunity, investigators seem well positioned to design and test candidate vaccines. Yet more recent studies of the role of a maternal immunity in the natural history of congenital HCMV infection, including the recognition that reinfection of previously immune women by genetically distinct strains of HCMV occur in populations with a high seroprevalence, have raised several questions about the nature of protective immunity in maternal populations. This finding coupled with observations that have documented a significant incidence of damaging congenital infections in offspring of women with immunity to HCMV prior to conception has suggested that vaccine development based on conventional paradigms of adaptive immunity to viral infections may be of limited value in the prevention of damaging congenital HCMV infections. Perhaps a more achievable goal will be prophylactic vaccines to modify HCMV associated disease in allograft transplant recipients. Although recent descriptions of the results from vaccine trials have been heralded as evidence of an emerging success in the quest for a HCMV vaccine, careful analyses of these studies have also revealed that major hurdles remain to be addressed by current strategies.

The Neonatal Fc receptor (FcRn) enhances human immunodeficiency virus type 1 (HIV-1) transcytosis across epithelial cells

The mechanisms by which human immunodeficiency virus type 1 (HIV-1) crosses mucosal surfaces to establish infection are unknown. Acidic genital secretions of HIV-1-infected women contain HIV-1 likely coated by antibody. We found that the combination of acidic pH and Env-specific IgG, including that from cervicovaginal and seminal fluids of HIV-1-infected individuals, augmented transcytosis across epithelial cells as much as 20-fold compared with Env-specific IgG at neutral pH or non-specific IgG at either pH. Enhanced transcytosis was observed with clinical HIV-1 isolates, including transmitted/founder strains, and was eliminated in Fc neonatal receptor (FcRn)-knockdown epithelial cells. Non-neutralizing antibodies allowed similar or less transcytosis than neutralizing antibodies. However, the ratio of total:infectious virus was higher for neutralizing antibodies, indicating that they allowed transcytosis while blocking infectivity of transcytosed virus. Immunocytochemistry revealed abundant FcRn expression in columnar epithelia lining the human endocervix and penile urethra. Acidity and Env-specific IgG enhance transcytosis of virus across epithelial cells via FcRn and could facilitate translocation of virus to susceptible target cells following sexual exposure.

HIV-1 causes a sexually transmitted disease. However, the mechanisms employed by the virus to cross genital tract tissue and establish infection are uncertain. Since cervicovaginal fluid is acidic and HIV-1 in cervicovaginal fluid is likely coated with antibodies, we explored the effect of low pH and HIV-1-specific antibodies on transcytosis, the movement of HIV-1 across tight-junctioned epithelial cells. We found that the combination of HIV-1-specific antibodies and low pH enhanced transcytosis as much as 20-fold. Virus that underwent transcytosis under these conditions was infectious, and infectivity was highly influenced by whether or not the antibody neutralized the virus. We observed enhanced transcytosis using antibody from cervicovaginal and seminal fluids and using transmitted/founder strains of HIV-1. We also found that the enhanced transcytosis was due to the Fc neonatal receptor (FcRn), which binds immune complexes at acidic pH and releases them at neutral pH. Finally, staining of human tissue revealed abundant FcRn expression on columnar epithelial cells of penile urethra and endocervix. Our findings reveal a novel mechanism wherein HIV-1 may facilitate its own transmission by usurping the antibody response directed against itself. These results have important implications for HIV vaccine development and for understanding the earliest events in HIV transmission.

Seminal plasma and semen amyloids enhance cytomegalovirus infection in cell culture

Among the modes of transmission available to the cytomegalovirus (CMV) is sexual transmission, primarily via semen. Both male-to-female (M-F) and male-to-male (M-M) sexual transmission significantly contribute toward the spread of CMV infections in the global population. Semen plays an important role in carrying the viral particle that invades the vaginal or rectal mucosa, thereby initiating viral replication. Both semen and seminal plasma (SP) can enhance HIV-1 infection in cell culture, and two amyloid fibrils, semen-derived enhancer of viral infection (SEVI) and amyloids derived from the semenogelins (SEM amyloids), have been identified as seminal factors sufficient to enhance HIV-1 infection (J. Munch et al., Cell 131:1059-1071, 2007; N. R. Roan et al., Cell Host Microbe 10:541-550, 2011; F. Arnold et al., J. Virol. 86:1244-1249, 2012). Whether SP, SEVI, or SEM amyloids can enhance other viral infections has not been extensively examined. In this study, we found that SP, SEVI, and SEM amyloids strongly enhance both human CMV (HCMV) and murine CMV infection in cell culture. SEVI and SEM amyloids increased infection rates by >10-fold, as determined by both flow cytometry and fluorescence microscopy. Viral replication was increased by 50- to 100-fold. Moreover, viral growth curve assays showed that SP, SEVI, and SEM amyloids sped up the kinetics of CMV replication such that the virus reached its replicative peak more quickly. Finally, we discovered that SEM amyloids and SEVI counteracted the effect of anti-gH in protecting against CMV infection. Collectively, the data suggest that semen enhances CMV infection through interactions between semen amyloid fibrils and viral particles, and these interactions may prevent HCMV from being neutralized by anti-gH antibody.

Cytomegalovirus in the neonate: immune correlates of infection and protection

Fetal and neonatal infections caused by human cytomegalovirus (CMV) are important causes of morbidity and occasional mortality. Development of a vaccine against congenital CMV infection is a major public health priority. Vaccine design is currently focused on strategies that aim to elicit neutralizing antibody and T-cell responses, toward the goal of preventing primary or recurrent infection in women of child-bearing age. However, there has been relatively little attention given to understanding the mechanisms of immune protection against acquisition of CMV infection in the fetus and newborn and how this information might be exploited for vaccine design. There has similarly been an insufficient study of what deficits in the immune response to CMV, both for mother and fetus, may increase susceptibility to congenital infection and disease. Protection of the fetus against vertical transmission can likely be achieved by protection of the placenta, which has its own unique immunological milieu, further complicating the analysis of the correlates of protective immunity. In this review, the current state of knowledge about immune effectors of protection against CMV in the maternal, placental, and fetal compartments is reviewed. A better understanding of immune responses that prevent and/or predispose to infection will help in the development of novel vaccine strategies.

FcRn-mediated intestinal absorption of IgG anti-IgE/IgE immune complexes in mice

BACKGROUND

The mechanism(s) responsible for the acquisition of maternal antibody isotypes other than IgG are not fully understood.

OBJECTIVE

To define the ability of the neonatal Fc receptor for IgG uptake (FcRn) to mediate intestinal absorption of IgG(1) anti-IgE/IgE immune complexes.

METHODS

C57BL/6 allergic ovalbumin (OVA)-immune foster mothers were generated to nurse naïve FcRn(+/-) or FcRn(-/-) progeny. At the time of weaning, serum levels of OVA-specific antibodies and IgG(1) anti-IgE/IgE immune complexes were determined in allergic foster mothers and FcRn(+/+), FcRn(+/-), or FcRn(-/-) breastfed offspring. In separate experiments, FcRn(+/-) or FcRn(-/-) neonatal mice were gavage fed TNP-specific IgE as IgG(1) anti-IgE/IgE immune complexes, IgG(1) isotype control and IgE, or IgE alone. Mice were killed 2 h after feeding to determine serum levels and biological activity of absorbed TNP-specific IgE.

RESULTS

As expected, the absorption of maternal OVA-specific IgG(1) in FcRn(-/-) offspring was at levels 10(3) -10(4) less than observed in FcRn(+/+) or FcRn(+/-) offspring. Surprisingly, FcRn expression also influenced the absorption of maternal IgE. OVA-specific IgE was detected in FcRn(+/+) and FcRn(+/-) offspring, but not in FcRn(-/-) offspring. IgG(1) anti-IgE/IgE immune complexes were detected in allergic foster mothers and correlated strongly with levels in FcRn(+/+) and FcRn(+/-) offspring (ρ = 0.88, P < 0.0001). Furthermore, FcRn expression was required for neonatal mice to absorb TNP-specific IgE when fed as IgG(1) anti-IgE/IgE immune complexes. When immune complexes were generated with IgG(1) anti-IgE directed against the Cε4 domain, the absorbed IgE was able to function in antigen-dependent basophil degranulation.

CONCLUSIONS AND CLINICAL RELEVANCE

These data demonstrate a novel mechanism by which FcRn may facilitate absorption of maternal antibodies other than IgG. These findings are clinically relevant because FcRn mediates the transplacental passage of maternal IgG to the fetus. This raises the possibility that FcRn could mediate the transplacental passage of maternal IgE as IgG anti-IgE/IgE immune complexes.

Epstein-Barr virus transcytosis through polarized oral epithelial cells

Although Epstein-Barr virus (EBV) is an orally transmitted virus, viral transmission through the oropharyngeal mucosal epithelium is not well understood. In this study, we investigated how EBV traverses polarized human oral epithelial cells without causing productive infection. We found that EBV may be transcytosed through oral epithelial cells bidirectionally, from both the apical to the basolateral membranes and the basolateral to the apical membranes. Apical to basolateral EBV transcytosis was substantially reduced by amiloride, an inhibitor of macropinocytosis. Electron microscopy showed that virions were surrounded by apical surface protrusions and that virus was present in subapical vesicles. Inactivation of signaling molecules critical for macropinocytosis, including phosphatidylinositol 3-kinases, myosin light-chain kinase, Ras-related C3 botulinum toxin substrate 1, p21-activated kinase 1, ADP-ribosylation factor 6, and cell division control protein 42 homolog, led to significant reduction in EBV apical to basolateral transcytosis. In contrast, basolateral to apical EBV transcytosis was substantially reduced by nystatin, an inhibitor of caveolin-mediated virus entry. Caveolae were detected in the basolateral membranes of polarized human oral epithelial cells, and virions were detected in caveosome-like endosomes. Methyl β-cyclodextrin, an inhibitor of caveola formation, reduced EBV basolateral entry. EBV virions transcytosed in either direction were able to infect B lymphocytes. Together, these data show that EBV transmigrates across oral epithelial cells by (i) apical to basolateral transcytosis, potentially contributing to initial EBV penetration that leads to systemic infection, and (ii) basolateral to apical transcytosis, which may enable EBV secretion into saliva in EBV-infected individuals.

Effects of immunization of pregnant guinea pigs with guinea pig cytomegalovirus glycoprotein B on viral spread in the placenta

BACKGROUND

Cytomegalovirus (CMV) is the most common cause of congenital virus infection. Infection of guinea pigs with guinea pig CMV (GPCMV) can provide a useful model for the analysis of its pathogenesis as well as for the evaluation of vaccines. Although glycoprotein B (gB) vaccines have been reported to reduce the incidence and mortality of congenital infection in human clinical trials and guinea pig animal models, the mechanisms of protection remain unclear.

METHODS

To understand the gB vaccine protection mechanisms, we analyzed the spread of challenged viruses in the placentas and fetuses of guinea pig dams immunized with recombinant adenoviruses expressing GPCMV gB and β-galactosidase, rAd-gB and rAd-LacZ, respectively.

RESULTS

Mean body weight of the fetuses in the dams immunized with rAd-LacZ followed by GPCMV challenge 3 weeks after immunization was 78% of that observed for dams immunized with rAd-gB. Under conditions in which congenital infection occurred in 75% of fetuses in rAd-LacZ-immunized dams, only 13% of fetuses in rAd-gB-immunized dams were congenitally infected. The placentas were infected less frequently in the gB-immunized animals. In the placentas of the rAd-LacZ- and rAd-gB-immunized animals, CMV early antigens were detected mainly in the spongiotrophoblast layer. Focal localization of viral antigens in the spongiotrophoblast layer suggests cell-to-cell viral spread in the placenta. In spite of a similar level of antibodies against gB and avidity indices among fetuses in each gB-immunized dam, congenital infection was sometimes observed in a littermate fetus. In such infected fetuses, CMV spread to most organs.

CONCLUSIONS

Our results suggest that antibodies against gB protected against infection mainly at the interface of the placenta rather than from the placenta to the fetus. The development of strategies to block cell-to-cell viral spread in the placenta is, therefore, required for effective protection against congenital CMV infection.

Fetal human cytomegalovirus transmission correlates with delayed maternal antibodies to gH/gL/pUL128-130-131 complex during primary infection

Primary human cytomegalovirus (HCMV) infections during pregnancy are associated with a high risk of virus transmission to the fetus. To identify correlates of intrauterine HCMV transmission, serial serum samples from HCMV transmitter and non-transmitter pregnant women with primary HCMV infection were analyzed for the presence of neutralizing antibodies against different glycoproteins and glycoprotein complexes, which are known to mediate entry into distinct types of host cells. Neutralizing activity was detected in the sera early after primary infection; absorption with a soluble pentameric complex formed by gH/gL/pUL128-131, but not with gH/gL dimer or with gB, abolished the capacity of sera to neutralize infection of epithelial cells. Importantly, an early, high antibody response to pentamer antigenic sites was associated with a significantly reduced risk of HCMV transmission to the fetus. This association is consistent with the high in vitro inhibition of HCMV infection of epithelial/endothelial cells as well as cell-to-cell spreading and virus transfer to leukocytes by anti-pentamer antibodies. Taken together, these findings indicate that the HCMV pentamer complex is a major target of the antibody-mediated maternal immunity.

The "silent" global burden of congenital cytomegalovirus

Human cytomegalovirus (CMV) is a leading cause of congenital infections worldwide. In the developed world, following the virtual elimination of circulating rubella, it is the commonest nongenetic cause of childhood hearing loss and an important cause of neurodevelopmental delay. The seroprevalence of CMV in adults and the incidence of congenital CMV infection are highest in developing countries (1 to 5% of births) and are most likely driven by nonprimary maternal infections. However, reliable estimates of prevalence and outcome from developing countries are not available. This is largely due to the dogma that maternal preexisting seroimmunity virtually eliminates the risk for sequelae. However, recent data demonstrating similar rates of sequelae, especially hearing loss, following primary and nonprimary maternal infection have underscored the importance of congenital CMV infection in resource-poor settings. Although a significant proportion of congenital CMV infections are attributable to maternal primary infection in well-resourced settings, the absence of specific interventions for seronegative mothers and uncertainty about fetal prognosis have discouraged routine maternal antibody screening. Despite these challenges, encouraging results from prototype vaccines have been reported, and the first randomized phase III trials of prenatal interventions and prolonged postnatal antiviral therapy are under way. Successful implementation of strategies to prevent or reduce the burden of congenital CMV infection will require heightened global awareness among clinicians and the general population. In this review, we highlight the global epidemiology of congenital CMV and the implications of growing knowledge in areas of prevention, diagnosis, prognosis, and management for both low (50 to 70%)- and high (>70%)-seroprevalence settings.

Human cytomegalovirus-induces cytokine changes in the placenta with implications for adverse pregnancy outcomes

Human cytomegalovirus (CMV) infection of the developing fetus can result in adverse pregnancy outcomes including death in utero. Fetal injury results from direct viral cytopathic damage to the CMV-infected fetus, although evidence suggests CMV placental infection may indirectly cause injury to the fetus, possibly via immune dysregulation with placental dysfunction. This study investigated the effects of CMV infection on expression of the chemokine MCP-1 (CCL2) and cytokine TNF-α in placentae from naturally infected stillborn babies, and compared these changes with those found in placental villous explant histocultures acutely infected with CMV ex vivo. Tissue cytokine protein levels were assessed using quantitative immunohistochemistry. CMV-infected placentae from stillborn babies had significantly elevated MCP-1 and TNF-α levels compared with uninfected placentae (p = 0.001 and p = 0.007), which was not observed in placentae infected with other microorganisms (p = 0.62 and p = 0.71) (n = 7 per group). Modelling acute clinical infection using ex vivo placental explant histocultures showed infection with CMV laboratory strain AD169 (0.2 pfu/ml) caused significantly elevated expression of MCP-1 and TNF-α compared with uninfected explants (p = 0.0003 and p<0.0001) (n = 25 per group). Explant infection with wild-type Merlin at a tenfold lower multiplicity of infection (0.02 pfu/ml), caused a significant positive correlation between increased explant infection and upregulation of MCP-1 and TNF-α expression (p = 0.0001 and p = 0.017). Cytokine dysregulation has been associated with adverse outcomes of pregnancy, and can negatively affect placental development and function. These novel findings demonstrate CMV infection modulates the placental immune environment in vivo and in a multicellular ex vivo model, suggesting CMV-induced cytokine modulation as a potential initiator and/or exacerbator of placental and fetal injury.

Cytomegalovirus impairs cytotrophoblast-induced lymphangiogenesis and vascular remodeling in an in vivo human placentation model

We investigated human cytomegalovirus pathogenesis by comparing infection with the low-passage, endotheliotropic strain VR1814 and the attenuated laboratory strain AD169 in human placental villi as explants in vitro and xenografts transplanted into kidney capsules of SCID mice (ie, mice with severe combined immunodeficiency). In this in vivo human placentation model, human cytotrophoblasts invade the renal parenchyma, remodel resident arteries, and induce a robust lymphangiogenic response. VR1814 replicated in villous and cell column cytotrophoblasts and reduced formation of anchoring villi in vitro. In xenografts, infected cytotrophoblasts had a severely diminished capacity to invade and remodel resident arteries. Infiltrating lymphatic endothelial cells proliferated, aggregated, and failed to form lymphatic vessels. In contrast, AD169 grew poorly in cytotrophoblasts in explants, and anchoring villi formed normally in vitro. Likewise, viral replication was impaired in xenografts, and cytotrophoblasts retained invasive capacity, but some partially remodeled blood vessels incorporated lymphatic endothelial cells and were permeable to blood. The expression of both vascular endothelial growth factor (VEGF)-C and basic fibroblast growth factor increased in VR1814-infected explants, whereas VEGF-A and soluble VEGF receptor-3 increased in those infected with AD169. Our results suggest that viral replication and paracrine factors could undermine vascular remodeling and cytotrophoblast-induced lymphangiogenesis, contributing to bleeding, hypoxia, and edema in pregnancies complicated by congenital human cytomegalovirus infection.

Human cytomegalovirus escapes a naturally occurring neutralizing antibody by incorporating it into assembling virions

Human cytomegalovirus (CMV) is a common but difficult to treat infection of immunocompromised patients. MSL-109 is a human monoclonal IgG isolated from a CMV seropositive individual that recognizes the viral glycoprotein H (gH) surface antigen complexes that mediate entry. Although MSL-109 blocks CMV infection in vitro, it lacked sufficient efficacy in human trials, and CMV isolated from treated patients suggested the evolution of MSL-109 resistance. To understand how CMV escapes MSL-109, we characterized a MSL-109-resistant CMV strain. Our results elucidate a nongenetic escape mechanism in which the antibody is selectively taken up by infected cells and incorporated into assembling virions in a dose-dependent manner. The resistant virus then utilizes the Fc domain of the incorporated antibody to infect naive nonimmune cells. This resistance mechanism may explain the clinical failure of MSL-109, illustrate a general mechanism of viral antibody escape, and inform antiviral vaccine and therapeutic development.

High susceptibility to cytomegalovirus infection of pregnant women in Flanders, Belgium

Maternal antibodies against cytomegalovirus (CMV) infection offer, to some extent, protection against congenital CMV infection. This study describes the seroprevalence of CMV-specific IgG in 220 parturient women during pregnancy, at delivery, at 3 months after delivery and in their cord blood (Flanders, Belgium, 2006-2008). ELISA was used to measure IgG. Of this population, 30% had positive IgG titres. Active transplacental transport was confirmed with a ratio 1.15/1. Elevated maternal IgG titre and increased parity, but not age, were significantly associated with higher seroprevalence of CMV-specific IgG in the cord blood. These data indicate a high susceptibility to CMV among fertile women. Prenatal prevention and other strategies to prevent intra-uterine infection are of critical importance in a highly susceptible population.

Modeling of human cytomegalovirus maternal-fetal transmission in a novel decidual organ culture

Human cytomegalovirus (HCMV) is the leading cause of congenital infection, associated with severe birth defects and intrauterine growth retardation. The mechanism of HCMV transmission via the maternal-fetal interface is largely unknown, and there are no animal models for HCMV. The initial stages of infection are believed to occur in the maternal decidua. Here we employed a novel decidual organ culture, using both clinically derived and laboratory-derived viral strains, for the ex vivo modeling of HCMV transmission in the maternal-fetal interface. Viral spread in the tissue was demonstrated by the progression of infected-cell foci, with a 1.3- to 2-log increase in HCMV DNA and RNA levels between days 2 and 9 postinfection, the expression of immediate-early and late proteins, the appearance of typical histopathological features of natural infection, and dose-dependent inhibition of infection by ganciclovir and acyclovir. HCMV infected a wide range of cells in the decidua, including invasive cytotrophoblasts, macrophages, and endothelial, decidual, and dendritic cells. Cell-to-cell viral spread was revealed by focal extension of infected-cell clusters, inability to recover infectious extracellular virus, and high relative proportions (88 to 93%) of cell-associated viral DNA. Intriguingly, neutralizing HCMV hyperimmune globulins exhibited inhibitory activity against viral spread in the decidua even when added at 24 h postinfection-providing a mechanistic basis for their clinical use in prenatal prevention. The ex vivo-infected decidual cultures offer unique insight into patterns of viral tropism and spread, defining initial stages of congenital HCMV transmission, and can facilitate evaluation of the effects of new antiviral interventions within the maternal-fetal interface milieu.

Neonatal Fc receptor and IgG-based therapeutics

The majority of potent new biologics today are IgG-based molecules that have demonstrated tissue-targeting specificity with favorable clinical response. Several factors determine the efficacy of these products, including target specificity, serum half-life and effector functions via complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity or drug conjugates. In this review, we will focus on the interaction between therapeutic antibody and neonatal Fc receptor (FcRn), which is one of the critical factors in determining the circulating antibody half-life. Specifically, we will review the fundamental biology of FcRn, FcRn functions in various organs, Fc mutations designed to modulate binding to FcRn, IgG-based therapeutics that directly exploit FcRn functions and tools and strategies used to study FcRn-IgG interactions. Comprehensive understanding of FcRn-IgG interactions not only allows for development of effective therapeutics, but also avoidance of potential adverse effects.

[Cytomegalovirus (CMV)]

Human cytomegalovirus (HCMV) is a ubiquitous beta human herpesvirus type 5. Compared to other human herpesviruses, HCMV is the largest, with a genome of approximately 235 kb containing approximately 250 ORFs with the potential to encode proteins. Usually, HCMV asymptomatically infects the host during childhood, and establishes life-long latency. The infection is life-threatening for infants and immunocompromised individuals, because of direct cytopathicity by viral replication, causing systemic organ injuries. Intrauterine infection occasionally causes microcephaly, sensorineural hearing loss and mental retardation. HCMV genome contains a number of accessory genes. Most of them are engaged in immune evasion or inhibition of cell death, possibly, resulting in a symbiosis between virus and host. CD34-positive myeloid progenitor cells are considered as a site of latency. However, the molecular mechanisms by which HCMV establishes and maintains latency and reactivates remain poorly understood. Recently in Japan, the decline of maternal HCMV seropositivity may increase the risk of intrauterine infection. It needs to immediately establish the protection against transplacental HCMV infection, such as a new type of neutralizing antibody or vaccine, which effectively interferes viral entry specific to endothelial and epithelial cells. Furthermore, HCMV infection might be considered as the most important factor for driving immune senescence in the elderly.

Cytomegalovirus infections during pregnancy

PURPOSE OF REVIEW

To review current prenatal diagnosis and management of congenital cytomegalovirus (CMV) infections with emphasis on maternal screening and available interventions.

RECENT FINDINGS

Recent findings include an enhanced understanding of the epidemiology, pathogenesis, and treatment of CMV infections; a knowledge of high-risk women particularly those with chronic exposure to a young child in the home; the availability of accurate methods for the serologic diagnosis of a primary CMV infection using either single or serial blood samples; accurate methods for the diagnosis of fetal infection via amniotic fluid; sensitive fetal and placental indicators for neonatal outcomes, and the availability of potentially effective interventions such as hygienic intervention and CMV hyperimmune globulin.

SUMMARY

These findings suggest that serologic testing for CMV during pregnancy may be appropriate either using one-time testing or serial serologic testing throughout the first two trimesters of pregnancy and that education of pregnant women about CMV is necessary so that they can asses their risk and make informed choices about serologic screening.

Extensive complement-dependent enhancement of HIV-1 by autologous non-neutralising antibodies at early stages of infection

BACKGROUND

Non-neutralising antibodies to the envelope glycoprotein are elicited during acute HIV-1 infection and are abundant throughout the course of disease progression. Although these antibodies appear to have negligible effects on HIV-1 infection when assayed in standard neutralisation assays, they have the potential to exert either inhibitory or enhancing effects through interactions with complement and/or Fc receptors. Here we report that non-neutralising antibodies produced early in response to HIV-1 infection can enhance viral infectivity.

RESULTS

We investigated this complement-mediated antibody-dependent enhancement (C'-ADE) of early HIV infection by carrying out longitudinal studies with primary viruses and autologous sera derived sequentially from recently infected individuals, using a T cell line naturally expressing the complement receptor 2 (CR2; CD21). The C'-ADE was consistently observed and in some cases achieved infection-enhancing levels of greater than 350-fold, converting a low-level infection to a highly destructive one. C'-ADE activity declined as a neutralising response to the early virus emerged, but later virus isolates that had escaped the neutralising response demonstrated an increased capacity for enhanced infection by autologous antibodies. Moreover, sera with autologous enhancing activity were capable of C'ADE of heterologous viral isolates, suggesting the targeting of conserved epitopes on the envelope glycoprotein. Ectopic expression of CR2 on cell lines expressing HIV-1 receptors was sufficient to render them sensitive to C'ADE.

CONCLUSIONS

Taken together, these results suggest that non-neutralising antibodies to the HIV-1 envelope that arise during acute infection are not 'passive', but in concert with complement and complement receptors may have consequences for HIV-1 dissemination and pathogenesis.

Human cytomegalovirus is protected from inactivation by reversible binding to villous trophoblasts

Human cytomegalovirus (HCMV) is the leading cause of congenital disease in the developed world. Transmission of HCMV to the fetus can occur through the villous placenta. Previously, we have shown that although syncytiotrophoblast (ST) can be productively infected, it is more likely that HCMV reaches the fetus through breaks in the ST than through basal release of progeny virus from infected ST. Progeny virus released on the maternal side could interact back with the ST and accumulate. In pregnancy, the organ distribution of disease burden is dramatically shifted, with the placenta reported as a reservoir for some pathogens. Thus, we propose that the ST layer functions as a viral reservoir, where HCMV is harbored and ultimately protected from degradation. Using primary cytotrophoblasts differentiated into an ST culture in vitro and challenged with HCMV, we have defined reversible binding between the virus and trophoblasts that protects the virus from degradation. This is blocked by treatment with low pH and neutralizing intravenous immunoglobulin. This reversible binding likely is to heparan sulfate proteoglycans, because heparin treatment blocks it. Importantly, we show that bound and released virus maintained in culture for at least 48 h results from inoculum and not progeny virus. Thus, the placenta has the potential to accumulate a relatively high steady-state level of virus within the intervillous space resulting from localized binding and release at the ST. A better understanding of the molecular interactions between HCMV and ST will provide insights regarding interventions to prevent or minimize congenital transmission.